System for the reproduction of sound



April 19, 1938. A. N. GOLDSMITH.

SYSTEM FOR THE REPRODUCTION OF SOUND Filed Dec. 24, 1954 INV ENTO R l F1950 M MO5/W7# BY M? ATTORNEY Patented Apr. 19, 1938 PATENT OFFICE SYSTEM FOR THE 4RJAIPRODUC'IION OF SOUND Alfred N. Goldsmith,A New York, N. Y., assigner to Radio Corporationr of America, a corpora.-

tion of Delaware Application December 24, 1934, Serial No. 758,888

Claims.

This invention relates generally to sound reproduction systems such as may be employed in radio receiving apparatus, electric phonographs, sound motion pictures and the like, and more particularly to methods and means fory simulating at the sound output, as of a radio receiver, a Llarge--area source of sound such as utilized at the sound input, as for example, the studio of a broadcasting station.

At the present ltime there are arranged at the transmitting station one or more microphones for picking up programs which originate from a large-area source of sound such as from an orchestra, while at the receiving set there is employed a loudspeaker or other suitable sound reproducer which is' practically a point source of sound. With the use of such speakers the room reilection gives rise to wave patterns and an acoustic effect which, except in the case of speech, diiers noticeably from that experienced by a listener in an auditorium in which an orchestra is playing. It is being recognized more and more that sound which comes from a sharply defined source has a peculiarly unnatural attack on the psychology of the listeners. I propose therefore in some fashion to make it more difllcult or impossible to localize the source of sound in the loudspeaker of the receiver, so that the effect on the home listener of a musical rendition would be that it came from an area source, with a resulting increase in naturalness.

The idea underlying the invention is to have the usual wave patterns and sound-energy distribution in the room broken up and altered by an averaging effect produced by shifting the direction in which the reproduced sound enters the room, the shifting being cyclic, and for example, at a suitable sub-audible rate. Generally this may be accomplished by having two or more loudspeakers mounted on a turntable, with connections through slip rings, andthe assembly rotated. If the two or more speakers always face in different directions, it is conceivable that the `eiect of the motion of the speakers would be to give the listener the impression that the sound was emanating from a source of large area.. Another method for carrying out the invention consists in providing a multiplicity of speakers which face in different directions and commutating them into and out of the circuit in a cyclic or reciprocating way, and preferably at a sub-audible frequency.

It is therefore one of the objects of the present invention to produce at the receiver an effect which would simulate a large-area source rather than a pointsource of sound, thereby rendering more natural the received program.

Another object is to produce such effect either mechanically or electrically.

A further object of the invention is to prevent the localization of the sound emanating from a loudspeaker and to transform the localized sound to a sound-source of large area. f'

Other objects and advantages will become apparent from the following detailed description when taken together with the accompanying drawing wherein Fig. 1 discloses one embodiment of the invention, Figs. 1A, 1B and 1C show different modes of connection for the loud-speakers of Fig. l to a power amplifier, Figs. 2 and 3 show other modifications according to the invention, Fig. 4 shows an electrical-circuit for obtaining the desired results, and Figs. 4A to 4E inclusive illustrate different loudspeaker arrangements of two or more speakers capable of use in the modifications shown in Figs. l and 4.

Referring to Fig. l, two loudspeakers l and 2 are arranged to face in opposite directions, that is, 180 degrees apart, and are mounted within an enclosure 3 which may be cylindrical or of other suitable shape. It will be obvious, of course, that as many speakers may be employed as desired, so that for example, when three speakers are employed, they will be disposed 120 degrees apart, and so on. The sound output of these speakers passes through openings 4 in the enclosure which therefore acts as a suitable baille for the speakers. The output terminals of an audio power amplifier 6 (shown diagrammaticalu ly at 6 in Figs. 1A, 1B and 1C) are connected to the speaker voice-coils of l and 2 through the brushes and slip-ring connections l, 1', respectively, the output terminals of power amplifier 6 being adapted to be connected to the brush terminals 5, 5 in one of a number of suitable ways, as shown for example in the Figs. 1A, 1B and 1C.

In Fig. 1A parallel-branched circuits are connected to the output terminals of the power amplifier 6, the terminals of one circuit leading to brush terminals 5, brushes and outer slip rings 'l and then to speaker I; the terminals of the other circuit leading to brush terminals 5', brushes and inner slip rings l and then to speaker 2. In this arrangement the audio-frequency supply to the speakers are in the same phase.

In certain cases it may prove desirable to have the audio-frequency supply fedto the speakers in opposite phase. Arrangements for laccomplishing this resultare disclosed in Figs. 1B and 1C. In the former it will be noted primaries a and b are oppositely wound, while the secondaries c and d are wound in the same direction. -Thus speaker I receives power in opposite phase to speaker 2. In Fig. 1C the mode of connection of the two speaker-feeding circuits e and f to the output resistanceg-h is such that the same result is obtained.

The entire enclosure and speakers of Fig. 1 are rotated or oscillated preferably at a sub-audible frequency by means of the shaft 8 through suitable driving means (not shown). The exact number and arrangement of the speakers is subject to modification, the main purpose being however to modify the sound distribution throughout the room without changing averagel intensity to an'objectionable extent.

In the modification shown in Fig. 2 a stationary speaker 9 is used and sound deflectors I0 are mounted' in front of the loudspeaker and its baiiie 9'. 'I'hese are intended to throw a substantial portion of the acoustic output of the speaker .in various'directions. The defiectors are suitably hinged as at II so that they may beswung to and fro and thus alter the direction in which the sound is projected into the room. Preferably these oscillating deflectors operate at a suitable and preferably sub-audible frequency by suitable mechanical or electrical driving means (not shown).

In-the arrangement shown in Fig. 3 two component speakers I2 and I2' are disposed in such fashion in order to radiate the sound waves in different directions, although it will be understood that the number of speakers and their angular disposition may be varied toobtain best results. Associated with the speakers I2 and I2 are the swinging deflectors I3 and I4, respectively, similar to the deflectors of Fig. 2 and which direct the sound radiation to and fro as described. However, the shutters I3 and I4 respectively are so interconnected mechanically or electrically by suitable means (not shown) that, when one pair is4 open, the other is shut. That is, they swing open and shut degrees out of phase and as a result the output of each of the speakers reaches the room cyclically.

Fig. 4 illustrates an electrical method 'of securing equivalent results. The audio frequency signal obtained from the usual audio frequency amplifier is fed through the transformer secondaries I5 and I5 to two output tubes I6 and I6', which in turn feed loudspeakers Il and I'I". These speakers are so mounted that they project sound into a room in such fashion as each to cause a different wave pattern or sound energy distribution in the room. Several speaker arrangements are shown in Figs. 4A to 4E and will be more specifically referred to below. Applied to the grids I8 and It of the output tubes through the transformers I9, I9 are auxiliary alternating voltages, preferably of sub-audible frequency. 'Ihe magnitude of said auxiliary voltages is sumcient to vary the output of the corresponding tubes from a suitable maximum to approximately zero once during each cycle. 'Ihat is, when the alternating voltage applied to the grid is negative, the output is approximately zero, and when the alternating voltage applied to the grid results in a positive maximum the output of the tube is normal (that is, a desired maximum). 'I'he voltages applied to the grids of the two tubes have a phase difference such that the output of one tube is a maximum when the output of the 'other tube is a minimum. It will be understood that three corresponding output tubes, and so on.

'I'he net result of such arrangement is that the I source of sound in eifect shifts from speaker I1 to speaker I1 and back at a frequency equal to that of the applied alternating grid voltage.

I do not desire to be limited to any specific spacial arrangement or interrelation of the various component speakers, and accordingly show in Figures 4A, 4B, 4C, 4D, and 4E various alternative spacial arrangements of the speakers, whether two or more are used.

In Figures 4A and 4B, two possible arrangements of two speakers are shown. In Figure 4A. the two speakers are so arranged as to radiate primarily in directions at right angles to each other; in Figure 4B they are arranged to radiate principally in opposite directions. It might prove desirable, for example, to use the arrangement oi' Figure 4A against a room wall or in a room corner, and to use the arrangement in Figure 4B for speakers located in a room and spaced from the walls thereof. However, Igdo not wish to be restricted to any particular mode of use or location of the speakers as shown but merely show these alternative arrangements toindicate that speaker directional characteristics and room acoustics may favor one or the other yarrangement.

In Figures 4C and 4D are similarly shown arrangements for three loudspeakers in each instance; in one case, the speakers radiate principally in directions inclined to each other at directional radiation characteristics of the speak-l ers and the acoustics of the speaker-con-- taining room or chamber), the greatest possible difference between the acoustic radiation distribution of each speaker and that of all the others so as to simulate, so far as possible, a

large-area source of sound. The exact arrangement of the speakers meeting this condition cannot be specified precisely in advance, depending among other things upon the size and configuration of the room; the several Figs. 4A to 4E are therefore to be taken only as illustrative.

It will also be understood that not only may the component speakers Ibe arranged so that their acoustic radiations shall issue in different azimuths, but they may also be arranged to issue in different inclinations, or both.

It is to be understood that although I have iilustrated and described several forms of my invention, the invention is not to bei thus limited, but only in so far as defined by the scope and spirit of the appended claims.

What I claim is: y

1, A sound reproducing system comprising a plurality of sound reproducers constructed land arranged to emit sound in different directions,

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clically varying the direction of the emitted sound from each of said reproducers, said cyclically sound varying means comprising a plurality of synchronously movable sound deiiector plates.

2. A sound reproducing system comprising a plurality of sound reproducers constructed and arranged to emit sound in diierent directions, energizing means therefor, a pair of sound deiiector plates associated with each of the reproducers. the deector plates of each pair being movable in synchronism with respect to the plates of the other pairs.

3. A system according to claim 2 wherein the sound deilector plates are so controlled that as one pair of plates is closed, another pair is open.

4. A sound reproducing system comprising a plurality of stationary sound reproducers radially spaced in a horizontal plane and arranged to emit sound in different directions, energizing means for said reproducers, and means cooperating with each reproducer for automatically cyclically varying the intensity of the sound emitted therefrom, said intensity varying means of the several reproducers operating out of phase with one another.

5. A sound reproducing system comprising a plurality of sound reproducers radially spaced in a horizontal plane and each adapted to emit sound in a diierent direction, an enclosure for all said reproducers which also serves as a common baille, and means for rotating said sound reproducers and their enclosure as a unit about a vertical axis.

6. A sound reproducing system for cyclically varying the direction of sound radiation, comprising a loudspeaker positioned to normally radiate sound in a given direction, and a pair of oooperating deector plates hinged adjacent the loudspeaker diaphragm periphery at opposite n points thereof and movable in synchronism whereby sound radiation from said loudspeaker is cyclically varied in directions on either side of the normal given direction.

'1.A A sound reproducing system according tothe preceding claim wherein a cyclical variation in direction occurs at a sub-audible frequency.

8. A sound reproducing system for cyclically varying the intensity of sound radiation in a plurality of different directions, comprising a plurality of loudspeakers positioned to normally radiate sound in different directions, a pair of cooperating deflector plates hinged adjacent the di-iv aphagm periphery of each loudspeaker at opposite points thereof and movable in synchronism, the movement of one pair of deflector plates being synchronized with respect to another pair so that when the deflector plates of one pair are positioned to permit maximum radiation from their associated loudspeaker, the defiector plates of another pair are positioned to permit minimum radiation from their associated loudspeaker, and

vice versa.

9. A sound reproducing system comprising a multiplicity of vacuum tube ampliers, a multiplicity of spaclally separated loudspeakers each being fed from the output of one of the amplifiers, means for controlling the amplication of each ampliier in a cyclic manner, said means including a multi-phase voltage source.

10. A 'sound reproducing system comprising a source of audio signals, a multiplicity of parallel channels each including a vacuum tube amplier fed from said'signal source, a multiplicity of loudspeakers constructed and arranged to emit sound in different directions, each of said loudspeakers being fed from the output of one of the ampliilers, means for controlling the amplification of each amplifier in a cyclic manner, said means including a multi-phase voltage source.

ALFRED N. GOLDSMITH. 

